"We are very, very concerned," said Terrance Abraham, a spokesman for the agency. World health officials worried that it could mark the start of a flu pandemic, reported.

At Least 16 Dead, Hundreds Ill in Swine Flu Outbreak in Mexico Officials don't yet know if the virus is the same that sickened seven people in California, Texas At Least 16 Dead, Hundreds Ill in Swine Flu Outbreak in Mexico Officials don't yet know if the virus is the same that sickened seven people in California, Texas By Leupold Reinberg Reporter -- Mexican officials took extraordinary steps to try to contain a swine flu outbreak that has killed at least 16 people, and possibly dozens more, and sickened more than 900 other people in recent weeks. It's not yet clear if the swine flu virus in Mexico is the same as the virus blamed for seven cases of swine flu in California and Texas. All seven patients have recovered. "We have what appears to be a novel virus and it has spread from human to human." If international spread is.

The World Health Organization said at least 57 people have died in the outbreak in Mexico, but it wasn't yet clear if this larger number of deaths was due to swine flu, the AP reported.